This invention relates to protection and anti-theft devices, and more particularly to anti-theft devices for use with appliances such as TV's and the like located in motels and other areas subject to an unusually high percentage of theft. More particularly, the apparatus of this invention is suitable for detecting when an appliance is both disconnected from its primary power source and subsequently moved.
Various types of circuitry and devices are already available and used for detecting theft of certain appliances and for providing alarms. These circuits are particularly useful and find their primary use in motels, hotels and the like for protecting expensive small items such as TV sets, radios, etc. The previous type of protection devices are of various types. Some of these prior art devices operate whenever the appliance or set is moved from a predetermined location whereas others operate whenever the appliance is disconnected from its electrical power source. Still others combine these techniques, and only sound the alarm when the appliance is both disconnected and moved from its predetermined location. However, as is discussed hereinafter each of these prior art devices is typically either unusually complex or expensive. For example, U.S. Pat. No. 3,484,775 issued to W. D. Cline on Dec. 16, 1969, discloses circuitry which is connected between a standard wall receptacle for a TV set or other electrical appliance and the power cord of the appliance itself. A provision is made so that the alarm box connected to the wall is not easily unplugged. However, when the appliance plug itself is removed from the alarm box the alarm is given. In operation, removal of the appliance plug from the alarm box closes a switch which activates an RF transmitter circuitry which uses the electrical power wiring of the motel or hotel itself to transmit a signal to a receiver at a central monitoring location such that an alarm may be sounded. However, as will be appreciated from a study of the device of this patent, all that needs to be done to defeat the protection offered by this device is to forceably remove the alarm box from the electrical power outlet itself prior to removing the plug of the appliance from the box. It will further be appreciated that a thief in the process of stealing such an appliance will not be concerned about causing damage to the wall or the electrical power system of the motel by forceably removing the alarm box. Thus, although the described device might be effective against the novice thief, it in no way would deter the professional thief.
Still another protective device is disclosed in U.S. Pat. No. 3,710,371 issued to Whalen et al on Jan. 9, 1973. According to this patent, the alarm device uses a sensitive triggering device which when displaced from a normal position an audible alarm is latched closed and cannot be silenced unless a correct procedure or key method is followed. Typically, such a device will be located on the interior of a TV set and uses a mercury switch to trigger the alarm. Although very sensitive, and not easily observed or defeated, this type device has its objectionable characteristics in the fact that the alarm may inadvertently be set off when no theft was intended. For example, an innocent occupant of a motel or hotel may either jar the TV set or simply be wanting to move it slightly from one position to another and set off the alarm. The embarrassment and subsequent anger of a motel or hotel occupant innocently setting off the alarm is readily apparent.
Still another complex protection system disclosed in U.S. Pat. No. 3,766,540 issued to Schapfer et al on Oct. 16, 1973, and having some similarity to the detection system of the Cline patent is available for large motel and hotel operations. According to this circuitry, each of the appliance or TV's to be protected require modification of the TV or appliance by connecting a quartz crystal oscillator across its terminals. A frequency modulated oscillator connected to a transmission line which connects all the appliances is employed to stimulate the crystals in sequence. A transmission receiver which operates at a selected frequency and phase keeps track of the operating crystals. An alarm or a visual display of a number indicates the time and place of removal of the appliance. The obvious disadvantage of this system is the required modification and the complexity of the transmission and monitoring.
Still another type circuitry which combines the advantages of the Whalen and the Cline circuitry is available in circuitry disclosed in U.S. Pat. No. 3,836,901 issued to Matto et al on Sept. 17, 1974. According to this patent, the circuitry is mounted entirely or partly within the device to be protected and includes and alarm circuit loop and a control loop. The control loop continuously determines whether or not the line cord of the appliance is connected to the wall socket. The control loop further determines if the appliance is being moved. Only when an appliance is both moved and disconnected from the alarm circuit is the alarm of this particular circuitry activated. According to the circuitry described in this patent, a reed switch is held open to deactivate the alarm circuitry whenever the appliance is connected to the wall plug. However, although the device described in the Matto et al patent is superior to the device described heretofore, it still requires the use of discrete and expensive components which are subject to short life.
In addition to the Matto et al, the Whalen et al, the Schopfer et al, and the Cline patents, an investigation of the prior art revealed several other patents related to the present invention. These patents include U.S. Pat. No. 3,045,226 issued to W. B. Trayner on July 17, 1962; U.S. Pat. No. 3,644,921 issued Duggan et al on Feb. 22, 1972; U.S. Pat. No. 3,794,989 issued to Manley et al on Feb. 26, 1974; U.S. Pat. No. 4,023,157 issued to Miller on May 10, 1977, and U.S. Pat. No. 4,121,201 issued to Weathers on Oct. 17, 1978. A review of these patents, quickly discloses that a great deal of effort and concern has been put into arriving at anti-theft devices for protecting TV sets and the like located in hotel and motel rooms. To date as mentioned above, all of the previous devices include certain objectionable characteristics.